How to query available domains?

[idyllhands]

Hi guys. Sorry, but I wasn't quite sure where to post this question, hopefully it's not inappropriate to post here.

I was wondering if anyone knows how sites likes www.instantdomainsearch.com query available domains. Do they perform a whois query? Or are there databases of non-registered domains available

[jasonJ]

I don't know the answers but you may be interested in this site: ajaxdomainsearch (http://www.ajaxdomainsearch.com/blog/).